According to officials, the relatively higher pollution level despite the continuous rain could be attributed to the cloudy weather and wind direction.

Officials said air quality in Noida, Ghaziabad and parts of NCR was better in the week preceding the rain and has improved after the rain in the past three days.(Sunil Ghosh / HT Photo )

The air quality in Noida, Ghaziabad and other parts of the National Capital Region (NCR) has remained in the ‘moderate’ category, despite six days of continuous rain last week, according to data from Central Pollution Control Board (CPCB).

While officials claim that air quality is usually good during the rain, as the major pollutant PM10 found in dust settles down, other pollutants now seem to be trapped in the atmosphere due to the continuous cloudy weather. Incidentally, air quality was better in the week preceding the rain and has improved after the rain in the past three days.

According to officials, the relatively higher pollution level despite the continuous rain could be attributed to the cloudy weather and wind direction.

“Throughout last week, the weather was cloudy and moisture-laden. In such conditions, it becomes difficult for the pollutants to escape the atmosphere, rather than when there is a clear sky. Additionally, wind speed was not very high and also oscillated between two directions in the NCR,” Kuldeep Srivastava, director, regional weather forecasting centre, India Meteorological Department, New Delhi, said.

So, the pollutants were also not blown away and remained in the atmosphere, he added.

Since the rainy weather started on September 2 and continued till September 8, the air quality index (AQI) for Noida as well as Ghaziabad remained between 100 and 150. On September 4, it reached ‘very poor’ at 304 in Noida. Before August 31, for over a week, the air quality in most NCR cities was between 50 and 100. On August 27, the air quality was in the ‘good’ category at less than 50 in Ghaziabad and Greater Noida, and similar levels were recorded for Noida on August 29.

Since the past three days, there has been no rain in Noida and consequently, the AQI has also improved. The AQI was ‘satisfactory’ on two days — 87 on September 7 and 76 on September 8 — in Noida. Pollution level in the city was recorded to be in the ‘poor’ category on September 9 and 10, but officials said that this was because of a fault in the PM2.5 recording monitor.

“This is a natural phenomenon across most of north India and it is difficult to immediately analyse what could be the cause. However, while the pollution levels have increased, they are still not high and have remained in the ‘moderate’ category,” Ashok Tiwary, regional officer of Uttar Pradesh Pollution Control Board (UPPCB), said.

The situation is similar in most NCR cities. On average, the AQI in Noida, Greater Noida, Ghaziabad, Gurugram, as well as Delhi was in the ‘moderate’ category all through last week between August 31 and September 5, but was lower and in the ‘satisfactory’ category the week before.

Interestingly, while PM10 is the prominent pollutant in Delhi-NCR through most of the year, other pollutants also contribute on some days. Through the past week, PM2.5 had been recorded as a prominent pollutant and nitrogen compounds were also high. Officials say that when these pollutants are higher in the air, the cause is vehicular pollution rather than construction dust.